Amazfit A1918 Compatible Battery 3.85V 350mAh Li-Polymer

Amazfit T-Rex / Verge Lite / A1918 — 3.85V Li-Polymer Replacement Battery (PL512524G)

This is a 3.85V, 350mAh Li-Polymer cell that replaces part number PL512524G in the Amazfit A1918, A1808, T-Rex, Verge Lite, and A1801 smartwatches. It fits when the original cell no longer holds charge after extended use or repeated shallow cycling. Dimensions are 24.00 × 24.20 × 5.30mm — measure your existing cell before ordering if you have an unknown revision.

• A1918, A1808, T-Rex, Verge Lite, A1801 compatibility: These five models share the same battery footprint, connector pinout, and BMS handshake voltage — all run the same PL512524G cell on a 3.85V nominal rail with matching protection thresholds.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the A1918 platform. The BMS accepted the cell without fault codes, protection cutoff triggered correctly at low voltage, and the fuel gauge IC registered charge state accurately after a full calibration cycle.
• Post-swap charging requirement: Place the watch on its charger immediately after fitting this cell and charge to 100% before using the watch. The fuel gauge IC on this platform loses its reference point when the cell is swapped and cannot read charge state accurately without a full charge cycle from near-zero.

Why the Verge Lite and T-Rex drain this cell faster in the first week

A new Li-Polymer cell has a slightly different internal impedance than a degraded original. The heart rate and SpO2 sensors on these models adjust their drive current based on signal return, and a fresh cell with lower impedance can cause the sensor subsystem to pull more current than usual during the first several charge cycles. This normalises once the fuel gauge IC recalibrates and the sensors settle on the new cell's impedance profile. No action is needed — full capacity and normal draw stabilise within five to seven days of regular use.

Watch shows 0% and will not wake after battery swap

This happens when the fuel gauge IC has lost its charge reference — a direct result of removing power during the swap. The IC does not fabricate a reading; it defaults to 0% when it has no valid state-of-charge data. Connecting the watch to its magnetic charger resets the IC and initiates a calibration cycle from the known near-zero starting point. Leave it on charge until it reads 100% — at that point the IC has a valid reference and normal battery indication resumes.